1. Field of the Invention
The present invention relates generally to image recording apparatuses, and more particularly to an image recording apparatus having a front/rear sheet face sensor for detecting a recording sheet being fed in upside down.
2. Description of the Prior Art
Various types of image recording apparatuses have heretofore been developed and used. One uses a photosensitive pressure-sensitive microcapsule sheet and an image receiving sheet wherein the microcapsule sheet is exposed to an imaging light to selectively photocure microcapsules to thus form a latent image thereon. The exposed microcapsule sheet is brought to facial contact with the image receiving sheet and a pressure is applied thereto in a pressure developing unit, with the result that the microcapsules which remain uncured are ruptured and chromogenic materials released therefrom react with a developer material coated on the image receiving sheet, thereby forming a visible output image on the image receiving sheet.
Since only one side of the image receiving sheet is coated with the developer material, feeding of the sheets into the apparatus is not reversible. If the sheet is fed upside down, no visible image is produced. Further, paper jam and machine troubles tend to occur resulting from an sheet face orientation error.
To obviate such troubles, it has been proposed to provide a sheet face sensor unit alongside a sheet conveying path. As shown in FIG. 1, the sensor unit includes a light emitting element 70 for emitting a light toward the surface of a recording sheet 74, and a light receiving element 72 disposed to receive the light reflected from the recording sheet 74. Based on an amount of light received at the light receiving element 72, the front or rear face of the sheet 74 is identified.
However, a sheet face identification error tends to occur after a long-term use of the apparatus due to change in amount of light emitted from the light emitting element or received at the light receiving element caused by aging or dust deposited on these elements.